Too much kern?
I think there is a mix up between the number of pairs for a font and a full family. 320 000 refer to the family. So, by font its more something around 25 000 pairs.
Again, 25 000 don’t make sense to people who don’t get that we are in OpenType era, with large character set, who include Caps, Small caps, Lowercases, alternates, many ligatures, and large support of language. There more glyphs than in a Type 1 font… All of this increase the possibilities, whatever you do, even if you have only very few kerns for the basic glyphs.
We may also know that we use at Porchez Typofonderie, like anyone doing correct OpenType fonts, kern classes. So, there is 900 real true plain kerns, but because of classes, it create many virtual kerns, that humans can’t create alone each by each. At the end, there is not so much more kerns in Parisine PTF than in the old Parisine (250 glyphs), just that with a larger glyph set, there is more glyphs (700), more possibilities.